1. Technical Field of the Invention
The present invention relates generally to an accumulator fuel injection system for internal combustion engines, and more particularly to an improved structure of such a system designed to avoid a failure in operation of a pressure relief valve caused by pressure pulsations of a drain line.
2. Background Art
Accumulator fuel injection systems are known which supplies a high-pressure fuel to an accumulator of a common rail through a supply pump and distributes the fuel stored in the accumulator to a plurality of fuel injectors installed one in each cylinder of an internal combustion engine. The accumulator fuel injection systems usually have a pressure relief valve connected to the accumulator of the common rail. FIG. 7 shows an example of such a pressure relief valve.
The pressure relief valve 100 works as a pressure limiter and consists essentially of a valve 101, a cylindrical housing 102, and a hollow screw 103. The valve 101 is made up of a valve body having a valve hole 111 formed therein and a valve ball 105 selectively opening and closing the valve hole 111.
The housing 102 has an inlet side fuel hole 112, a small-diameter hole 113, and an outlet side fuel hole 114. Within the inlet side fuel hole 112, a spring guide 107 and a spring 108 are disposed which urge the valve ball 105 to close the valve hole 111 at all times. The hollow screw 103 has formed therein a longitudinal hole 115 communicating with the outlet side fuel hole 114 and a lateral hole 116 extending perpendicular to the longitudinal hole 115. The lateral hole 116 communicates with a fuel passage 117 in a low-pressure pipe 109 (i.e., a drain line) through which the fuel is returned back to a fuel tank (not shown).
A valve-opening pressure at which the ball valve 105 is to be opened is determined by a contact area between the valve body 104 and the valve ball 105 and a set load produced by the spring 108. The valve-opening pressure may be adjusted by changing the thickness of shims 118 and 119. The lateral hole 116 of the hollow screw 103 has a fuel-flowing sectional area substantially identical with that between the valve 101 and the longitudinal hole 115 of the hollow screw 103.
If some flow resistance exists in the low-pressure pipe 109, it may cause pressure pulsations of the fuel returned from the supply pump or the fuel injector back to the fuel tank through the low-pressure pipe to be transmitted to the valve 101 of the pressure relief valve 100, so that the valve ball 105 bounces within the valve body 104, thereby resulting in a change in valve-opening pressure of the pressure relief valve 100.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an improved structure of an accumulator fuel injection system capable of avoiding a failure of a pressure relief valve caused by pressure pulsations occurring in a drain line.
According to one aspect of the invention, there is provided an accumulator fuel injection apparatus which may be employed in a common rail system for diesel engines. The accumulator fuel injection apparatus comprises: (a) a high-pressure supply pump pumping fuel out of a fuel tank, the high-pressure supply pump pressuring and discharging the fuel; (b) an accumulator storing therein the fuel discharged from the high-pressure supply pump; (c) a fuel injector injecting the fuel stored in the accumulator into an internal combustion engine; (d) a high-pressure fuel line extending from the high-pressure supply pump to the fuel injector through the accumulator; (e) a relief valve having an inlet communicating with the high-pressure fuel line, an outlet, and a valve mechanism disposed between the inlet and the outlet, the valve mechanism being responsive to a rise in pressure of the fuel within the high-pressure fuel line beyond a given level to establish communication between the inlet and the outlet for relieving the rise in pressure of the fuel within the high-pressure fuel line; and (f) a pressure pulsation absorbing mechanism disposed between the valve mechanism of the relief valve and a pressure pulsation source existing downstream of the outlet of the relief valve. The pressure pulsation absorbing mechanism works to absorb a pressure pulsation propagated from the pressure pulsation source to the valve mechanism of the relief valve, thereby avoiding an undesirable change in a valve-opening pressure at which the valve mechanism opens the inlet to drain the fuel within the accumulator.
In the preferred mode of the invention, the valve mechanism includes a valve body in which the inlet of the relief valve is formed and a valve member movable to open and close the inlet selectively. The relief valve includes a hollow cylindrical housing having a fuel hole formed between the inlet and the outlet. The pressure pulsation absorbing mechanism includes a hollow screw which is fitted in an open end of the housing as defining the outlet of the relief valve and has formed therein an orifice working to absorb the pressure pulsation to be propagated from the pressure pulsation source to the valve mechanism. A valve-urging mechanism is disposed in the fuel hole of the housing which urges the valve member to close the inlet constantly.
The hollow screw includes a sleeve and a flange head. The sleeve is retained within the open end of the housing and has formed therein a longitudinal chamber communicating with the fuel hole of the housing through an end of the sleeve. The flange head is formed on an end of the sleeve opposite the housing.
The orifice is implemented by a hole formed in the sleeve which extends perpendicular to the longitudinal chamber of the sleeve. The hole is smaller in diameter than the fuel hole of the housing and the longitudinal chamber of the sleeve.
The relief valve communicates at the inlet thereof with the accumulator for relieving a rise in pressure of the fuel within the accumulator beyond the given level to keep the pressure in the accumulator constant.
The relief valve may alternatively communicate at the inlet thereof with an outlet of the high-pressure supply pump for relieving a rise in pressure of the fuel flowing into the accumulator beyond the given level to keep the pressure of the fuel supplied to the accumulator constant.
The relief valve may alternatively communicate at the inlet thereof with a portion of the high-pressure fuel line extending from the accumulator to the fuel injector for relieving a rise in pressure of the fuel supplied to the fuel injector beyond the given level to keep the pressure of the fuel supplied to the fuel injector constant.
According to another aspect of the invention, there is provided an accumulator fuel injection apparatus which comprises: (a) a high-pressure supply pump pumping fuel out of a fuel tank, the high-pressure supply pump pressuring and discharging the fuel; (b) an accumulator storing therein the fuel discharged from the high-pressure supply pump; (c) a fuel injector injecting the fuel stored in the common rail into an internal combustion engine; (d) a high-pressure fuel line extending from the high-pressure supply pump to the fuel injector through the accumulator; (e) a relief valve having an inlet communicating with the high-pressure fuel line, an outlet, and a valve mechanism disposed between the inlet and the outlet, the valve mechanism being responsive to a rise in pressure of the fuel within the high-pressure fuel line beyond a given level to establish communication between the inlet and the outlet for relieving the rise in pressure of the fuel within the high-pressure fuel line; and (f) a check valve disposed between the valve mechanism of the relief valve and a pressure pulsation source existing downstream of the outlet of the relief valve. The check valve works to block transmission of a pressure pulsation from the pressure pulsation source to the valve mechanism of the relief valve.
In the preferred mode of the invention, the valve mechanism includes a valve body in which the inlet of the relief valve is formed and a valve member movable to open and close the inlet selectively. The relief valve includes a hollow cylindrical housing having a fuel hole formed between the inlet and the outlet. A hollow screw is provided which is fitted in an open end of the housing as defining the outlet of the relief valve and has disposed therein the check valve. A valve-urging mechanism is disposed in the fuel hole of the housing which urges the valve member to close the inlet constantly.
The check valve includes a valve body, a check valve member, and a check valve-urging mechanism. The valve body has an orifice formed downstream of the fuel hole of the housing of the relief valve in communication therewith. The check valve-urging mechanism urges the check valve member into constant engagement with the orifice of the valve body.
The relief valve communicates at the inlet thereof with the accumulator for relieving a rise in pressure of the fuel within the accumulator beyond the given level to keep the pressure in the accumulator constant.
The relief valve may alternatively communicate at the inlet thereof with an outlet of the high-pressure supply pump for relieving a rise in pressure of the fuel flowing into the accumulator beyond the given level to keep the pressure of the fuel supplied to the accumulator constant.
The relief valve may alternatively communicate at the inlet thereof with a portion of the high-pressure fuel line extending from the accumulator to the fuel injector for relieving a rise in pressure of the fuel supplied to the fuel injector beyond the given level to keep the pressure of the fuel supplied to the fuel injector constant.